HIGH-TEMPERATURE DECONTAMINATION AND UTILIZATION OF PHOSPHOGYPSUM

Algimantas Kazragis

doi:10.3846/16486897.2004.9636835

Abstract

Waste piles of phosphogypsum formed from deposits of phosphoric acid production by‐product loom near the city of Kedainiai in the center of Lithuania. Every year about 250 thousand tons of this by‐product were gathered when the plant was in full operation. At present, about 13 to 15 million tons of phosphogypsum have accumulated which is mainly gypsum dihydrate – (95–98) %, however, contaminated with phosphoric and fluoric acids as well as with other hazardous admixtures what makes this raw material ecologically harmful and also hampers the use of phosphogypsum instead of natural gypsum for the production of binding materials. These materials pollute the environment. Phosphogypsum can be “deacidified” with lime and then treated as normal natural gypsum to obtain hemi hydrate gypsum. However, good‐quality binding materials were not obtained in this case. Heating of phosphogypsum up to a temperature of 600 °C provides for the decomposition and elimination of binding obstruction admixtures. Heating to 1000 °C and higher temperatures causes the decomposition of the former with the formation of an activator in anhydrite lime and thus anhydrite cement. In general, the utilization of this environmentally harmful waste and the binding of toxic pollutants can contribute to the solution of environmental problems in the central region of Lithuania.

Highlights

As various branches of industry metallurgy, energy, construction materials, food and others as well as transport develop more and more harmful gases, such as CO2, CO, SO2, NO, NO2, HCl, Hydrogen fluoride (HF), not fully combusted hydrocarbons, inorganic and volitile organic acids, organic solvents, the constituent parts of varnishes and paints vapours and gases are emitted into the atmosphere.Lithuanian researchers, including those from Vilnius Gediminas Technical University, Department of Environmental Protection, have conducted many investigations over the past years to evaluate various inert and toxic pollutant concentrations in the air [18], atmospheric precipitation [9] wastewater, in ponds and natural water basins and in the soil [1015]
In 19631973 not far from the city of Këdainiai in the center of Lithuania four sulphuric acid production lines were put into operation as well as those for the production of conventional and granulated superphosphate, aluminum fluoride, phosphoric acid, amofose and other fertilizer mixtures
It is formed during the manufacture of phosphoric acid by reacting the mineral apatite brought from Khibini region, Russia, with sulphuric acid according to the following reaction: 3Ca3 (PO4 )2 ⋅ CaF2 +10H2SO4 + 20H2O =

Summary

Introduction

As various branches of industry metallurgy, energy, construction materials, food and others as well as transport develop more and more harmful gases, such as CO2, CO, SO2, NO, NO2, HCl, HF, not fully combusted hydrocarbons, inorganic and volitile organic acids, organic solvents, the constituent parts of varnishes and paints vapours and gases are emitted into the atmosphere. Joint-Stock Company Palemono keramika during the period 19891992 and in 1997 manufactured a novel anhydrite cement composition according to the technology developed by Institute of Architecture and Construction [23] This material was produced from the following raw materials: JSC Lifosa (Këdainiai) dihydrate non-acidic phosphogypsum (pH = 9,89,3) (79,0 79,5) %; Krûnas deposit clay 16 %; neutralized JSC Ekranas (Panevëþys) glass slime (kinescope glass polishing waste) containing SiO2 and R2O 4 %; Ca(OH) from JSC Ventos SM (0,51,0) %; water.

Experimental investigation

Testing methods

Thermodynamic analysis of anhydrite thermal decomposition

Decomposition of phosphogypsum admixtures during heating

Binding properties of phosphogypsum sintered up to 1000 oC

Kazragis